At issue was a provision of state law that permits one voter to challenge another’s registration, a provision that activist groups used to try to disenfranchise thousands of voters in three North Carolina counties before the 2016 election. The challenges were filed and processed in large batches, making the activity tantamount to a voter purge — the often-flawed process by which election officials remove large numbers of voters from registration lists.

In November 2016, federal district court Judge Loretta Biggs issued a preliminary injunction against the practice after the North Carolina NAACP and others brought suit, saying that it likely violated the National Voter Registration Act of 1993 (NVRA).

During a hearing on the preliminary injunction, Judge Biggs said she was “horrified” by the “insane” process in which voters were disenfranchised without their knowledge. The law allows individuals to easily file hundreds or even thousands of challenges at the same time, with little evidence to support the claims. In many cases, a piece of returned mail was the only basis. “This looks like something that was put together in 1901,” she said, referring to the state’s Jim Crow laws.

Judge Biggs recognized that calling the process a “challenge” doesn’t exempt voters from federal protections. A voter purge by any other name smells just as fishy.

Wednesday’s order permanently blocks the removals unless the voter is given notice and a waiting period, and unless the removals happen at least 90 days before federal elections. Although the ruling was not a surprise given the history of the case, it does provide some insights on how careless voter purges can affect voters and how the law — if enforced — can protect them.

Here are three insights from the order:

1. Important federal protections against voter purges remain.

Many expressed concern at the Supreme Court’s June decision in Husted v. A. Philip Randolph Institute,which upheld Ohio’s controversial practice of using failure to vote in a single election to initiate a purge process. The decision allows voters to be purged when there is not a strong basis for determining ineligibility, as the Brennan Center and the League of Women Voters noted in an amicus brief. Nonetheless, as the North Carolina decision shows, the decision was not a greenlight to purge at will.

One critical safeguard is the requirement of a notice and a two-election waiting period before voters can be considered to have moved and therefore be deleted from the rolls. Husted expressly upheld this requirement, and Judge Biggs cited the case for that proposition. An Indiana federal judge blocked a state law (which uses the Crosscheck program to immediately purge voters) on the same basis only days before the Court issued its Husted ruling.

Another protection is the requirement that systematic purges — ones that remove large numbers of voters without meaningful individualized inquiry — must be completed at least 90 days before an election. This is critical to allow voters time to catch and correct errors.

2. Laws that allow challenges to voter registration are prone to abuse.

Although the order will prevent mass challenges without proper protections, “challenger” laws remain vulnerable to abuse in North Carolina and the 14 other states that have them. (Many more also allow challenges at the polls.) Although these laws are designed with individual cases in mind, the North Carolina incident shows how they can be abused to conduct voter purges without adhering to the requirements of federal law. Hancock County, Georgia, tried something similar before being challenged in court. Election officials in Colorado and Iowa have also tried to use a challenge process to purge large numbers of voters.

These efforts have either been rebuffed or abandoned when questioned, but the methods remain in place. Allowing one citizen to challenge another’s voter registration, with little or no evidence, and then forcing the challenged voter to re-prove their eligibility — when they have already gone through the process of registering to vote — is unfair and vulnerable to abuse.

3. Activist groups threaten voting rights but can be thwarted.

The North Carolina case also shows the damage “voter integrity” activists can cause when unchecked. A few self-appointed voter fraud vigilantes almost deprived thousands of their voting rights.

These organizations have pressured hundreds of counties nationwide to aggressively purge their rolls, sometimes problematically. In Noxubee County, Mississippi, two of these groups successfully forced an aggressive purge after the county could not marshal the resources to defend itself. Yet, when these groups meet resistance, such as in Broward County, Florida, they are far less successful.

This is exactly what happened in North Carolina. When the challenges themselves were challenged in court, they could not withstand legal scrutiny. Yesterday’s ruling is a reminder that vigilance is necessary and fighting for voting rights can pay off.